ALSA: hda - hdmi: Allow HDA patches to customize more operations

Upcoming AMD multichannel support requires many customized operations
(channel mapping, ELD, HBR) but can otherwise share most of its code
with the generic patch.

Add a local struct hdmi_ops containing customizable HDMI-specific
callbacks and move the current code to those callbacks. Functionality is
unaltered.
Signed-off-by: Anssi Hannula <anssi.hannula@iki.fi>
Signed-off-by: Takashi Iwai <tiwai@suse.de>